Die coaters for dispersing or otherwise forming a layer of material on a sheet or web are known in the art. For example, die coaters are used often in the production of pressure sensitive materials such as labels. In such case, a die coater is used to apply an adhesive layer on a web of liner material in the construction of the pressure sensitive material. The adhesive can be a liquid adhesive, an emulsion based adhesive, solvent based adhesive, or a solid hot melt adhesive, for example.
In a conventional type of die coater, a web material is run along a backup roll as a die applies a material such as an adhesive on the surface of the web. The die is located adjacent the backup roll and includes a slot through which the material to be applied is extruded. As the material exits the slot, the material is applied to the web which is supported by the backup roll. Typically, die coaters are designed to operate at high speeds on the order of 1000 to 1500 feet of web per minute or even higher.
The width of the web and the type of material which is to be applied to the web can vary from job to job. Typically, the backup roll preferably has a width which is approximately equal to the width of the web. As a result, different width webs require different width backup rolls. Moreover, oftentimes different materials which are to be applied through the die are non-compatible. It is therefore necessary to clean the die thoroughly prior to introducing a different, non-compatible, material into the die.
The task of replacing the backup roll with a backup roll having a different width has required significant down time in the past. The running of the web must be stopped and the labor intensive task of replacing the backup roll must be carried out prior to restarting the web run or beginning a new web run. This typically involves physically removing the original backup roll and replacing it with another backup roll. The web must then be rerouted through the die coater prior to restarting the coating process. This procedure for changing the backup roll can take an hour or more and results in a severe reduction in production efficiency.
Similarly, if it becomes necessary to switch from applying one material through the die to another material which is non-compatible with the original material, it has been necessary in the past to shut down the die coater in order to clean out the die. Again production efficiency suffered as a result. An option in the past has been to remove the original die and to replace it with a clean die for applying the non-compatible material. Unfortunately, this also required that the die coater be shut down for a substantial amount of time. Furthermore, in a die coater the alignment between the backup roll and the die is important to the operation of the apparatus. Thus, the replacement die must be carefully aligned to ensure proper alignment with respect to the backup roll. This results in additional down time to perform the adjustments necessary to ensure such alignment.
The amount of down time associated with changeovers between backup rolls and/or dies in conventional die coaters has become an even more serious problem in view of an increase in the industry in short orders, i.e., short runs of web. This has resulted in a need for more frequent changeovers between roll widths and/or dies.
Often an oven is used to cure the web and adhesive thereon. Nonuniform heating and possibly damage to the web and/or coating can occur if the time in the oven changes, e.g., due to down time while a roll or die is being changed or adjusted. Overcuring during down time can cause the web to become brittle resulting in web breaks and reduced production.
Efforts to eliminate the down time associated with changing rolls and/or dies have included the development of modular based die coater systems. In conventional modular systems, the backup roll remains in a main frame while the die for applying the material is housed in a removable module. Different modules including different dies can be exchanged with one another in the main frame. A drawback with such modular systems is that there still is substantial downtime associated with removing one module from the main frame and inserting another. Furthermore, the modules can weigh on the order of three thousand pounds to five thousand pounds and are difficult to maneuver even in the event the modules are mounted on casters. Also, the repeated removal and insertion of the modules can result in the die becoming misaligned relative to the backup roll.
Other known modular systems have attempted to overcome the misalignment problem by including the backup roll and the die together in a removable module. Again, however, changing the backup roll and die module requires substantial down time. Moreover, it is necessary to cut the web first in order to remove the module, and to splice or refeed either the previous web or a new web through the die coater after the new module has been inserted. It is not possible to avoid having to cut the web when changing modules and simply splice a new web material as is often desired. This system also has the same problems as above in relation to non-uniform heating due to down time.
In view of the aforementioned shortcomings associated with conventional die coaters, it will be appreciated that there is a strong need in the art for a die coater which does not involve substantial down time when changing over between backup rolls and/or dies. In particular, there is a strong need in the art for a universal die coater which changes between different backup rolls and/or different dies rapidly and automatically while preserving the precision alignment therebetween. Moreover, there is a strong need for a die coater which does not require that the web be cut and rerouted through the die coater during a changeover of the dies or rolls or require that the web run be stopped during a changeover.